Generally, when completing a subterranean well for the production of fluids, minerals, or gases from underground reservoirs, several types of tubulars are placed downhole as part of the drilling, exploration, and completions process. These tubulars can include casing, tubing, pipes, liners, and devices conveyed downhole by tubulars of various types. Each well is unique, so combinations of different tubulars may be lowered into a well for a multitude of purposes.
A subsurface or subterranean well transits one or more formations. The formation is a body of rock or strata that contains one or more compositions. The formation is treated as a continuous body. Hydrocarbon deposits may exist within the formation. Typically a wellbore is drilled from a surface location, placing a hole into a formation of interest. Completion equipment is placed downhole after drilling, including casing, tubing, and other downhole equipment as needed. Perforating the casing and the formation with a perforating gun is a well known method in the art for accessing hydrocarbon deposits within a formation from a wellbore.
Explosively perforating the formation using a shaped charge is a widely known method for completing an oil well. A shaped charge is a term of art for a device that when detonated generates a focused explosive output. This is achieved in part by the geometry of the explosive in conjunction with an adjacent liner. Generally, a shaped charge includes a metal case that contains an explosive material with a shape and has a thin metal liner on the inner surface of the explosive material. Many materials are used for the liner including brass, copper, tungsten, and lead. When the explosive detonates the liner metal is compressed into a super-heated, super pressurized jet that can penetrate metal, concrete, and rock.
A perforating gun typically has a gun body. The gun body typically is composed of metal and is cylindrical in shape. Within a typical gun tube is a charge holder or carrier tube, which is a tube that is designed to hold the actual shaped charges. The charge holder contains cutouts called charge holes where the shaped charges are placed.
A shaped charge is typically detonated by a booster or igniter. Shaped charges may be detonated by electrical igniters, pressure activated igniters, or detonating cord. One way to ignite several shaped charges is to connect a common detonating cord that is placed proximate to the igniter of each shaped charge. The detonating cord is comprised of material that explodes upon ignition. The energy of the exploding detonating cord can ignite shaped charges that are properly placed proximate to the detonating cord. Often a series of shaped charges may be daisy chained together using detonating cord.
An alternative to using a perforating gun with a gun body is a strip system where the perforating charges are exposed to the downhole environment. The strip system may be conveyed downhole using coiled tubing. A strip system is smaller in diameter and allows for the perforation of casing where size is an issue. The strip system typically may include a series of shaped charges strung together along a loading strip. These shaped charges typically are individually sealed against the downhole environment. When the perforating charges are fired the system may break up, leaving debris inside the wellbore. The remains of the loading strip and anything attached is then removed from the wellbore.